Wireless communication networks are widely deployed to provide various communication services such as voice, packet data, broadcast, and messaging. These wireless networks are typically capable of supporting communication for multiple users by sharing the available network resources. With today's networks, a number of different technologies (protocols) are employed for coding, processing, modulating and otherwise conditioning the communications signals. These technologies include but are not limited to: Global System for Mobile Communications (GSM); Code Division Multiple Access (CDMA); Wideband Code Division Multiple Access (WCDMA); and Long Term Evolution (LTE). To take advantage of the various network deployments, multi-mode phones have been developed with capability to communicate on two or more incompatible technologies.
Because of the limited frequency spectrum allocated for commercial communications on the current wireless networks, some of these technologies transmit and/or receive over the same frequency band in common geographical locations. As more technologies co-exist in the same band and multi-mode phones become more popular, initial acquisition becomes more and more challenging and time consuming for a specific technology. At the subscriber terminal (User Equipment or “UE”), acquisition failure (i.e., failure to establish communication on an available channel) has been become more common due to interference from other co-existing technologies. Each technology is limited by its own receiver (RX) front end in terms of bandwidth and dynamic range.
When a UE is first powered on and service information from the network is unavailable or invalid, the UE normally scans all of the valid carrier frequencies (or channels) in its network to attempt system acquisition via one of those carriers. Typically, it senses the raw power for each channel and makes a decision, based on a power threshold, whether to proceed with a full acquisition or to ignore that channel. For the Universal Mobile Telecommunications System (UMTS) Personal Communication Service (PCS) band, which has a 60 MHz bandwidth and a channel raster (spacing between adjacent carrier frequencies) of 200 kHz, the UE would search over 300 channels in the acquisition attempt. Because a power measurement carries no information on the underlying modulation, processing time and battery current are often wasted on attempts to acquire on irrelevant technologies.
Recently, there have been instances of GSM users reporting acquisition failure due to strong CDMA channels co-existing in the same band, even though there were strong GSM channels available. CDMA users have also reported acquisition issues due to confusion caused by GSM channels. As the spectrum becomes more crowded, the interference caused by other technologies will only get worse. Therefore, a need exists to mitigate the deleterious effects of such interference.